It is well known to even the average golfer that the equipment used in playing the game is subject to a great deal of friction, impact, and other stresses during a typical round of golf. Both the performance and the useful life of such equipment would benefit from the use of materials having increased durability. For instance, many types of golf clubs, such as putters, drivers, and wedges, contain polymer inserts in the face of the club. Since the club face directly strikes a golf ball thousands of times over the life of the club, improved durability is of great importance. Additionally, club components, such as shafts, grips, and hosels, undergo significant stress during a golf swing and contact with a golf ball and, therefore, could stand to benefit from more durable materials.
Of course, golf balls are repeatedly struck against very hard objects as well, including golf clubs, and it is very desirable to maintain their performance properties over as long a period of time as possible. Golfers of all skill levels seek out a variety of properties in their golf balls for a variety of golfing situations, although resilience, durability, and longevity are always important. The type of materials used in forming the different golf ball layers can greatly affect these properties, as well as the “click,” “feel,” spin, initial velocity, “playability,” and other properties.
Golf equipment is typically formulated from a variety of different materials. Most conventional materials, however, do not entirely address the problems associated with stress, durability, and repeated impact. Therefore, it is clear that improved materials, having material properties that address these preferred physical requirements, are necessary.
In addition, the manner in which golf equipment, or components thereof, is fabricated can affect certain properties of the materials, for example, such as durability. The types of chemistries present in the golf equipment materials can also sometimes indicate or dictate the preferred method of fabrication used to form them.
Particularly with respect to polyurethane-containing materials, commercially available golf equipment or components, especially for golf balls, can be currently made by casting or injection molding processes. The nature of current casting processes is such that materials that require a relatively long time (in comparison to other fabrication methods) to sufficiently solidify, i.e., react thoroughly. As a result, materials or compounds with particular chemistries that react or solidify relatively quickly are generally restricted from use in commercial casting processes, particularly in the golf art.
By using an alternative fabrication technique, reaction injection molding, as opposed to traditional injection molding, thermosetting materials and/or materials with relatively quick reaction or solidification times can be processed into certain articles. Reaction injection molding processes, due to the nature of the chemistries of the materials used, tend to result in decreased fabrication times, and can facilitate a decrease in the cost of fabricating such articles. The technique of reaction injection molding (RIM) using a variety of materials has been demonstrated in various publications.
For example, U.S. Pat. No. 4,762,322 discloses golf clubs with heads that can be made from a hollow metal shell or a low density, high strength material, such as a reaction injection molded polyurethane, formed around weighted inserts.
With respect to manufacture of golf balls, RIM has been disclosed, for example, in International Publication No. WO 00/57962, which claims golf balls, and processes for making such balls, comprising a reaction injection molded material, such as polyurethanes/polyureas.
In addition, U.S. Pat. No. 6,083,119 discloses a multi-layer golf ball with an inner and outer cover layer, at least one of which can contain a reaction injection molded polyurethane material.
U.S. Pat. Nos. 4,695,055 and 4,878,674 also disclose illuminated, translucent golf balls having a permanent diametric hole into which a chemiluminescent light stick is added, so that the golf balls may be visible in the dark. These golf balls can be fabricated by a method such as reaction injection molding.
Additionally, conventional non-reactive injection molding can be used to form relatively thin layers of material in golf equipment, or components thereof, generally in golf balls. Examples of thin components or layers made by conventional non-reactive injection molding have also been demonstrated in various publications.